Roof Area Calculator

1. Choose your units

2. Enter building dimensions

Building length (ft)

Building width (ft)

Eave overhang per side (in) Assumes the same horizontal overhang on all four sides.

3. Choose roof shape

Roof type A standard gable roof has two main sloped planes. This estimate assumes a rectangular plan and the same pitch across the roof.

4. Set roof pitch

Pitch (rise per 12 inches of run)

:12

For example, a 6:12 pitch rises 6 inches for every 12 inches horizontally.

5. Material allowance (optional)

Extra material for cuts and waste

This allowance affects the material-planning figure, not the roof's actual surface area.

Measure the building's length and width at the roof-plan level, including any consistent horizontal overhang if you prefer to measure roof dimensions directly.
Enter the horizontal overhang per side. If your dimensions already include the overhang, enter zero to avoid counting it twice.
Select the closest standard roof shape, then enter the roof pitch as rise per 12 inches of horizontal run.
Review the estimated sloped area. Add a material-waste allowance for a rough purchasing estimate.

Plan area = (length + 2 × overhang) × (width + 2 × overhang).

Slope multiplier = √(1 + (pitch ÷ 12)²).

Sloped roof area = plan area × slope multiplier.

Area with allowance = sloped roof area × (1 + waste percentage ÷ 100).

Designed for a regular rectangular roof plan with one consistent pitch. For standard gable, hip, and shed roofs, the total area formula is the same when the horizontal plan and pitch are the same; roof shape selection provides context but does not change the result.
Does not separately model dormers, valleys, multiple roof sections, irregular footprints, curved roofs, or different pitches. For complex roofs, calculate each regular section separately and add the results; avoid double-counting overlaps.
Gable-end walls are not included because this tool estimates roof surfaces, not vertical wall areas.
The waste percentage is a planning allowance, not a prediction of exact material usage. Product coverage, roof details, local practices, and manufacturer instructions can change the amount needed.
Results are not a substitute for on-site measurements or a qualified roofing professional's assessment.